Split sleeve cold expansion of fastener holes and other openings in structural members is a process in which a tapered mandrel is used in conjunction with a disposable, internally lubricated split sleeve, to compressively prestress a significant zone in the material surrounding the opening. This compressive prestressing offsets the stress concentration of the hole itself to produce substantial improvement in structural fatigue performance of the material on which the opening is formed.
Split sleeve cold expansion is most often performed on one side of the workpiece. The mandrel has a rear end portion which is connected to a piston within a puller tool. Starting from the rear end, and moving forwardly, the mandrel includes in order, a small diameter portion, an increasing diameter portion and a maximum diameter portion. The piston is retractable to retract the mandrel and is extendible to extend the mandrel. A split sleeve is moved endwise over the maximum and increasing diameter portions of the mandrel and onto the small diameter portion of the mandrel. The split in the sleeve allows the sleeve to expand as it is moved relatively over the maximum in creasing diameter portions of the mandrel. When the sleeve is on the small diameter portion of the mandrel it is contracted and has an outside diameter equal to or slightly smaller than the maximum diameter portion of the mandrel. The maximum diameter portion of the mandrel is sized to fit through a workpiece opening that is to be expanded. The split sleeve, while in a contracted position on the small diameter portion of the mandrel, is also fittable through the workpiece opening.
As a first step of a cold expansion method, as it has been practiced to date, a mandrel is extended out from the puller tool. Then, a split sleeve is hand installed onto the mandrel and is moved onto the exposed portion of the small diameter portion of the mandrel. Then the puller tool is hand moved to align the maximum diameter portion of the mandrel with the hole in the workpiece. Next, the puller tool is hand moved endwise to move the mandrel and sleeve into the hole. This endwise movement of the puller tool is continued until the split sleeve is within the hole and a nose piece on the puller tool is against the workpiece. The puller tool is then operated to retract the piston and the mandrel. Movement of first the increasing diameter portion and then the maximum diameter portion of the mandrel through the split sleeve causes another expansion of the split sleeve. The split sleeve thickness is significantly greater than the clearance between the maximum diameter portion of the mandrel and the wall of the workpiece opening. As a result, movement of the in creasing and maximum diameter portions of the mandrel through the split sleeve poses on the split sleeve a radially outward which acts on the workpiece material immediately surrounding the opening and increases the diameter of the opening. The diameter of the opening is increased a significant amount to introduce a compressive hoop prestress into the material surrounding the opening. The puller tool is operated to pull the mandrel completely through the split sleeve. Then, the puller tool is hand pulled by the operator away from the workpiece while the split sleeve remains in the workpiece. After cold expansion, and after movement of the puller tool and mandrel away from the workpiece, the used sleeve is removed from the opening as an additional step.
A principal object of the present invention is to provide a method and apparatus for facilitating the placement of a split sleeve on a mandrel, prior to cold working, and for easily and automatically removing the used sleeve from the hole following cold expansion, in response to movement of the puller tool and mandrel away from the workpiece.
The prior art processes and tooling are described in detail U.S. Pat. No. 3,566,662 , granted Mar. 2 , 1971, to Louis A. Champoux; U.S. Pat. No. 4,187,708, granted Feb. 12, 1980, to Louis A. Champoux; and U.S. Pat. No. 4,425,780, granted Jan. 17, 1984, to Louis A. Champoux. U.S. Pat. No. 4,583,388, granted Apr. 22, 1986, to Franciscus Hogenhout, discloses a puller tool for a split mandrel. The above patents, and the following additional U.S. patents, should be considered for the purpose of putting the present invention into proper perspective relative to the prior art. U.S. Pat. No. 3,892,121, granted Jul. 1, 1975, to Louis A. Champoux, Horace E. Hill and Joseph L. Phillips; U.S. Pat. No. 4,423,619, granted Jan. 3, 1984, to Louis A. Champoux; U.S. Pat. No. 4,471,643, granted Sep. 18, 1984, to Louis A. Champoux and Charles M. Copple; U.S. Pat. No. 4,524,600, granted Jun. 25, 1985, to Robert L. Champoux and Charles M. Copple; and U.S. Pat. No. 4,557,033, granted Dec. 10, 1985 to Robert L. Champoux.